The use of spray-drying to produce powders from fluid feed stocks is well known, with applications ranging from powdered milk to bulk chemicals and pharmaceuticals. See U.S. Pat. No. 4,187,617 and Mujumbar et al., 91 Drying, pages 56-73 (1991). The use of spray-drying to form solid amorphous dispersions of drugs and concentration-enhancing polymers is also known. See commonly owned European Patent Applications Nos. 0 901 786, 1 027 886, 1 027 887, 1 027 888, and commonly owned PCT Applications Nos. WO 00/168092 and WO 00/168055.
A typical spray-drying apparatus comprises a drying chamber, atomizing means for atomizing a solvent-containing liquid feed into the drying chamber, a source of heated drying gas directed into the drying chamber and dried product collection means for separating the dried product from the cooled drying gas and vaporized solvent stream following its exit from the drying chamber. Examples of such apparatus include Niro Models PSD-1, PSD-2 and PSD-4 (Niro A/S, Soeborg, Denmark). When used for forming solid amorphous dispersions by spray-drying, conventional wisdom suggests that to achieve the rapid removal of solvent required to form a homogeneous solid amorphous dispersion, the droplets of atomized solvent-containing feed should be small. The prior art therefore uses spray-drying apparatus equipped with a two-fluid nozzle for atomizing the solvent-containing feed, which produces droplets of solvent-containing feed with diameters of about 50 μm or less, resulting in a spray-dried product with median particle diameters of about 30 μm or less. In some cases such spray-drying apparatus are reported to be effective in forming substantially amorphous and substantially homogeneous solid amorphous dispersions of drug and polymer that exhibit concentration enhancement when introduced to an environment of use. In other cases, less than satisfactory results are achieved, thereby requiring undue experimentation to attempt to identify suitable process conditions. However, even when solid amorphous dispersion particles are successfully achieved, the spray-dried particles produced in such apparatus often have small median particle sizes (less than about 30 μm) and a large amount of “fines” (particles with diameters of less than about 10 μm). In addition, such particles often have high specific volumes—that is, the volume of the spray-dried powder divided by its mass—typically reported in units of cm3/g. Generally, the higher the specific volume of a powder, the poorer its flow characteristics. As a result, solid amorphous dispersions produced using a spray-drying apparatus equipped with a two-fluid nozzle have relatively poor flow characteristics and poor collection efficiency. In addition, downstream handling and processing of such small diameter, high specific volume products is often difficult.
Thus, there is a need in the art for an improved spray-drying process that results in solid amorphous dispersions with improved flow characteristics and improved collection efficiency.